1. Field of the Invention
This invention relates to cyclonic separation apparatus.
2. Related Background Art
Cyclonic separators are well known apparatus for removing particles from a gas flow without the use of filters. Cyclone separators have found utility in the field of vacuum cleaners to separate dirt and dust from the airflow. It is well known that the separation efficiency of cyclonic separators is dependent upon the force which is applied to the particles in the airflow, in accordance with the following formula.f=2mv2/d, where                f=the force applied to the particles        m=the mass of the particle        v=the flow velocity        d=the diameter of the cyclonic airflow        
Thus it will be appreciated that the separation efficiency is inversely proportional to the diameter of the cyclone chamber, such that smaller diameter cyclones are more suited to separating lighter particles than larger cyclones.
Accordingly, it is well known for vacuum cleaners to incorporate a first upstream stage, comprising a relatively large diameter cyclone having a maximum diameter of approximately 200 mm, and a plurality of parallel-connected downstream cyclones having a maximum diameter of approximately 20 mm. In use, the upstream cyclone separates course dirt and dust from the airflow, whereas the downstream cyclones separate the finer dirt and dust.
Vacuum cleaners of the above-mentioned type are disclosed in EP1361815, U.S. Pat. No. 3,425,192 and GB2406067 and comprise a plurality of small cyclones mounted in an array above or adjacent the larger upstream cyclone. A main airflow duct leads from the outlet of the upstream cyclone, the duct branching into a plurality of secondary ducts feeding one or more of the respective downstream cyclones.
One disadvantage of the above-mentioned arrangement is that the main duct can cause a restriction in the air flow and the resultant drop in air flow velocity reduces the separation efficiency. Another disadvantage of the above-mentioned arrangement is that the secondary ducts are complex, small and susceptible to blockage.